Suppression of pupillary unrest by general anesthesia and propofol sedation

Abstract

The pupil undergoes irregular oscillations when exposed to light. These oscillations, known as pupillary unrest in ambient light, originate from oscillatory activity within the Edinger-Westphal nucleus in the midbrain. The midbrain and upper pons also contain nuclei known to be very sensitive to the effects of anesthetics that play a central role in maintaining wakefulness. We hypothesized that anesthetics may display similar effects on wakefulness and pupillary unrest. Repeat measurements of pupillary unrest using infrared pupillometry were performed in 16 patients undergoing general anesthesia and 8 patients undergoing propofol sedation. Pupil scans were analyzed using fast Fourier transformation to quantify the effects of the anesthetics on pupillary unrest. During general anesthesia and deep sedation, observed pupillary unrest values below 0.1 (AU) indicate complete suppression of pupillary oscillations. Pupillary unrest decreased more during general anesthesia [to 24% of baseline (95% CI 17-30%)] than pupil size [51% of baseline (95% CI 45-57%)]. Sedation with propofol was associated with a reduction in pupillary unrest that was correlated to the depth of sedation as assessed by the Richmond Agitation-Sedation Scale and the processed electroencephalogram. Pupillary unrest is caused by oscillatory activity within the midbrain that is affected by the state of wakefulness or by hypnotics directly. Increased sedation and general anesthesia reduce and then abolish pupillary unrest as wakefulness decreases. We speculate that midbrain nuclei responsible for wakefulness and pupillary unrest are either communicating or share a similar sensitivity to the effects of commonly used anesthetics.